1. Field of the Invention
The present invention relates to a traveling carriage for use with devices, for example, a mobile robot, an automotive vehicle and a toy, which run or travel using driven wheels.
2. Description of the Prior Art
Traveling carriages which are movable in all directions are known including, for example, Japanese First (unexamined) Patent Publication Nos. 59-711 and 59-128610. The typical structure is shown in the latter publication and will be briefly explained with reference to FIGS. 22 to 24.
In the figures, a traveling carriage 1 includes left and right driven wheels 5, a pair of electric motors 6 for driving the corresponding driven wheels 5, respectively, and a rotary plate 3 holding the driven wheels 5 and the motors 6. Electromagnets 13 are further provided for prohibiting rotation of the rotary plate 3 during normal running of the traveling carriage 1. The traveling carriage 1 further includes four jacks for raising a carriage body 8 from a running surface 15 when the rotary plate 3 rotates to change a traveling direction of the traveling carriage 1.
During normal running, the electromagnets 13 are energized so that the rotary plate 3 is fixedly held against the carriage body 8 due to the attraction force of the energized electromagnets 13. In this state, the traveling carriage 1 runs straight by rotating the left and right driven wheels 5 in the same direction.
To run the traveling carriage 1 laterally, the electromagnets 13 is de-energized to release the attraction force applied to the rotary plate 3. Subsequently, the four jacks 12 are extended to raise the carriage body 8 relative to the running surface 15 with the driven wheels 5 remaining on the running surface 15. Accordingly, the carriage body 8 and the rotary plate 3 are spaced apart from each other. In this state, when the left and right driven wheels 5 are rotated in opposite or reverse directions from each other, the driven wheels 5 run on the running surface 15 so as to rotate the rotary plate 3 about a rotation shaft 9. When the rotary plate 3 is rotated by a desired angle, for example, by 90.degree., the jacks 12 are contracted to lower the carriage body 8. Subsequently, the electromagnets 13 are energized to hold the carriage body 8 and the rotary plate 3 firmly together. By rotating the left and right driven wheels 5 in the same direction in this state, the traveling carriage 1 runs straight laterally, that is, changing the traveling direction by 90.degree..
However, in the traveling carriage 1, when the running surface 15 is not fiat with recessed portions P present on the running surface 15 as shown in FIG. 23, frictional forces between the driven wheels 5 and the running surface 15 are reduced so as to possibly disable rotation of the rotary plate 3. Further, the traveling carriage 1 uses four jacks 12 for separating the carriage body 8 and the rotary plate 3 from each other. However, usage of four jacks inevitably makes the structure complicated. Further, when extending or contracting the jacks 12, particular control is necessary for operating all the jacks 12 simultaneously. Moreover, in the traveling carnage 1, two driven wheels 5 are arranged relative to one rotary plate 3. Accordingly, as shown in FIG. 24, in order to rotate the rotary plate 3 about a rotation center 121, a rotation radius R2 should be set relatively large. Since the rotary plate 3 along with the driven wheels 5 is arranged to rotate about the rotation center 121 within the carriage body 8, the carriage body 8 should be increased in size correspondingly. On the other hand, when the driven wheels 5 are arranged to be steered independently of each other for reducing the rotation radius of the rotary plate 3, an offset in steering phase is likely to occur between the left and right driven wheels 5, resulting in unstable running of the traveling carriage.